1. Field of the Invention
This invention relates to the use of silicone microemulsions in conjunction with silicone macroemulsions to produce high polymer content emulsions of lower than normal viscosity.
2. Background Information
Findley and Weyenberg developed methods of forming stable polymeric emulsions from siloxane oligomers. Their methods are taught in U.S. Pat. No. 3,294,725. issued Dec. 27, 1966.
Johnson et al. developed a silicone emulsion which gave an elastomeric product upon removal of the water, as shown in U.S. Pat. No. 4,221,688, issued Sept. 9, 1980. The dispersed phase comprised an anionically stabilized hydroxylated polydiorganosiloxane and a colloidal silica.
Another aqueous silicone emulsion is described in U.S. Pat. No. 4,244,849, issued Jan. 13, 1981, which provides an elastomeric product upon removal of the water under ambient conditions. The dispersed phase is a graft copolymer of a hydroxyl endblocked polydiorganosiloxane and an alkali metal silicate.
Emulsions having particle sizes in the range of below 0.1 micrometers (1000 Angstroms) have been developed.
Cekada and Weyenberg prepared colloidal suspensions of silsesquioxanes by adding silane to a water-surfactant mixture with agitation, at a slow rate as described in U.S. Pat. No. 3,433,780, issued Mar. 18, 1969.
A surface active composition which may be used as an emulsifier with diorganopolysiloxanes to form transparent microemulsions or transparent gels is described in U.S. Pat. No. 3,975,294, issued Aug. 17, 1976 and in U.S. Pat. No. 4,052,331, issued Oct. 4, 1977.
A unique method for the preparation of oil-in-water microemulsions is described in U.S. Pat. No. 4,146,499, issued Mar. 27, 1979. The four step process uses two different surfactants which are selected based upon their solubility in the oil phase and in the water phase.
A method of preparing polyorganosiloxane emulsions having small particle size is taught in U.S. Pat. No. 4,620,878, issued Nov. 4, 1986. A translucent oil concentrate is prepared by mixing a polar group containing polyorganosiloxane, surfactant and water. The concentrate is then rapidly dispersed in water to form a microemulsion with an average particle size of less than 0.14 micrometers.
Graiver and Tanaka developed methods of making stable silicone microemulsions by emulsion polymerization. Their methods are taught in U.S. application Ser. No. 809,090, filed Dec. 12, 1985.
In any of these methods, as the solids content of the emulsion is raised, the viscosity of the emulsion rises. For applications which require a flowable emulsion, the rise in viscosity limits the polymer content which can be achieved.